In mobile communications, a control channel may be utilized to inform mobile terminals regarding resource allocation, modulation, coding, hybrid automatic repeat request (HARQ) information, transmit power control (TPC) commands, etc. For example, a long-term evolution (LTE) network utilizes a physical downlink control channel (PDCCH) to communicate with and to provide such information to the mobile terminals. In an LTE network, the mobile terminals may utilize a blind detection technique to identify the PDCCH that is communicating with the respective mobile terminals. In this regard, blind detection may be utilized since multiple PDCCHs may be present in a single sub-frame and since a relatively large number of PDCCH transmission formats are supported.
The information provided via a control channel may include downlink control information (DCI). In addition, the information provided via the control channel may include a cyclic redundancy check (CRC) of the other information provided via the control channel. For example, a 16-bit CRC code may be included with the control channel information. An identifier, such as a radio network temporary identifier (RNTI), may be implicitly encoded in the CRC code and may therefore also be included with the control channel information.
In operation, the mobile terminals monitor the control channel and control channel information may be identified to be directed to a respective mobile terminal if the CRC is determined to be correct and the identifier, such as the RNTI, that is implicitly encoded in the CRC code matches an identifier associated with or otherwise monitored by the respective mobile terminal. In this regard, a mobile terminal generally monitors one or more identifiers, such as RNTIs, based upon the transmission mode of the mobile terminal.
Although an analysis of the CRC code, such as a 16-bit CRC code, is utilized to determine if the control channel information is directed to a respective mobile terminal, it is possible that some random bit sequences that are not, in fact, directed to the respective mobile terminal, may successfully pass the CRC check such that the associated control channel information will be incorrectly considered to be directed to the mobile terminal. This situation may result in a “false accept” in which the mobile terminal operates, at least for some period of time, under the mistaken determination that the control channel information was directed to the respective mobile terminal. For a 16 bit CRC code, the theoretical rate per sub-frame for false accepts is the product of 2−16, the number of decoding attempts and the number of identifiers, such as RNTIs, that are monitored by the respective mobile terminal. As such, each active mobile terminal may, in one example, experience a false accept once or twice per second by evaluating the control channel information in such a manner that the mobile terminal mistakenly determines that the control channel information is directed to the mobile terminal.
False accepts can degrade network performance. For example, a mobile terminal may falsely determine that control channel information that provides an uplink grant is directed to the respective mobile terminal. In this situation, the mobile terminal may transmit uplink data via an uplink identified by the uplink grant even though the uplink was actually intended to be granted to another mobile terminal. Since the network generally will not accept the uplink data erroneously transmitted by the mobile terminal in this situation, the mobile terminal may sometimes re-transmit the uplink data prior to the HARQ functionality restoring the state of the mobile terminal and avoiding any further erroneous transmissions via the uplink. However, the transmission of uplink data by the mobile terminal prior to the restoration of the state of the mobile terminal may cause at least some network performance loss, such as by unnecessarily increasing the signaling load on the network and/or potentially interfering with data transmitted by another mobile terminal via the same uplink. Additionally, the mobile terminal may also miss or fail to detect other control channel information that is actually intended for the respective mobile terminal while the mobile terminal falsely accepts and mistakingly acts upon control channel information that is intended for another mobile terminal.